Beware. There are pirates at preschool.
They have a pirate ship and have outfitted it with cannons.
The cannons shoot cannon balls. Just roll a ball down the pipe, stand back and wait for the explosion.
The beauty of having a myriad loose parts in a playground - and the time and freedom to use them as they please - is that the children can carry out their complex play scenarios in endless creative and imaginative ways.
They can see their ideas through to fruition independently, without having to break their play to seek adult assistance or risk pesky adult interference.
Sometimes - like this one - we only see evidence of their play after the fact.
Play is a child's business. Loose parts help them get on with it.